1. Field of the Invention
The invention relates generally to photomasks employed for fabricating microelectronic products. More particularly, the invention relates to phase shift photomasks employed for fabricating microelectronic products.
2. Description of the Related Art
Microelectronic products are formed incident to successive photolithographic processes that are employed for forming microelectronic devices and patterned microelectronic structures over microelectronic substrates.
The successive photolithographic processes employ photomasks for purposes of exposing blanket photoresist layers when forming patterned photoresist layers. In turn, the patterned photoresist layers are employed for forming the microelectronic devices and patterned microelectronic structures. Of the types of photomasks that may be employed when fabricating microelectronic products, phase shift photomasks are particularly desirable insofar as phase shift photomasks employ photoexposure light phase shifting such as to provide enhanced resolution of photoexposure light and thus enhanced resolution of patterned photoresist layers. Of the types of phase shift photomasks that may be employed when fabricating microelectronic products, alternating phase shift photomasks are common. Alternating phase shift photomasks are related to conventional photomasks that employ a patterned opaque material layer upon a transparent substrate to provide alternating transmissive regions and non-transmissive regions of the transparent substrate. However, alternating phase shift photomasks also employ a pit within alternating transmissive regions of the transparent substrate separated by the patterned opaque material layer. The pit is typically formed of a depth to provide a 180 degree phase shift of a photoexposure light beam for adjacent transmissive regions when employing the phase shift photomask.
While alternating phase shift photomasks are common and highly desirable in the microelectronic product fabrication art, they are nonetheless not entirely without problems. In that regard, while alternating phase shift photomasks do provide enhanced resolution of photoexposure light, they nonetheless also often provide the enhanced resolution with attendant optical asperities, such as ghost images.
It is thus desirable to provide phase shift photomasks with enhanced optical performance. The invention is directed towards the foregoing object.